1. Field of the Invention
The present invention relates to a dynamic coupling device to transmit a rotatory motion between two shafts.
Such a device can be widely used in many fields. It can, for example, be used in place of traditional friction clutches to connect the drive shaft to the transmission shaft in a motor vehicle, or in any situation in which it is necessary to connect the ends of two shafts so as to transmit a torque from one shaft to the other while maintaining the possibility of breaking said connection and restoring it at any moment depending upon requirements.
2. Prior Art
It is known that the most used devices to dynamically connect two rotating shafts can be classified in the following categories:
claw clutches;
friction clutches;
electromagnetic clutches;
hydraulic clutches or couplings.
Claw clutches substantially consist of members carried respectively by the two shafts to be connected, provided with mating projections or claws which can engage into each other so as to be driven in rotation.
Claw clutches can transmit very high torques while maintaining very reduced sizes but, on the other hand, they can get engaged only when the relative speed between the two shafts is very slow, or when one of the parts to be connected has a very reduced moment of inertia with respect to the axis of rotation.
Friction clutches transmit a torque between two shafts by utilizing the friction which develops between the surfaces of two or more elements that are pushed against each other and are integral with either shaft respectively. Unlike claw clutches, friction clutches also allow connection between shafts rotating at different speeds, and therefore they are widely used to achieve the connection between a drive shaft in motion and another shaft which is initially stationary.
Friction clutches however suffer the disadvantage that they lose large amounts of energy during the transitory steps in which the driven shaft increases its rotational speed as far as said speed reaches the same value as that of the drive shaft. Actually during these steps sliding inevitably occurs between the contact surfaces of the elements that are pushed against each other, which sliding causes a dissipation of energy in the form of heat and also causes the contact surfaces to be greatly worn out.
Electromagnetic clutches carry out the transmission of motion from a shaft to another by utilizing the electromagnetic induction which is produced between a cylindrical sleeve fastened to one of the shafts and a coil integral with the other shaft and disposed in coaxial relation within the sleeve.
Also clutches of this type allow connection between a rotating shaft and a shaft which is initially stationary. In addition, by suitably adjusting the intensity of the current passing through the coil it is possible to restrain, depending upon requirements, the maximum torque value which can be transmitted from a shaft to another.
These clutches too however have a drawback, that is the high weight and bulkiness they must possess so as to be able to transmit comparatively high torques. In addition, the operation of the electromagnetic clutch brings about an important waste of electric energy.
In hydraulic clutches or couplings, the movement and torque between the shafts are transmitted by effect of the hydrodynamic actions that are generated between bladed elements respectively integral to the two shafts, and a fluid held in a box containing the bladed elements.
Hydraulic clutches as well allow connection between a drive shaft in motion and a second shaft initially stationary.
The main drawback of this type of clutches is given by the occurrence of an important waste of energy in heat, above all when the relative speeds between the shafts are high as a result of losses by friction due to the molecular cohesion of the fluid.
A further drawback resides in the impossibility of entirely transmitting the movement of the drive shaft to the driven shaft when a resisting moment is applied to the latter.
In addition, hydraulic clutches are very complicated in construction, which involves high costs and they must also have big sizes and an important weight so that they may be able to transmit comparatively high torques.
From the foregoing it will be seen that each of the different types of clutches described above has some peculiar qualities which, depending upon the situation, make its use suitable in place of another type. However each type of clutches has drawbacks as well which must necessarily be accepted.
It is also to be noted that no one of the above described devices is adapted to maintain a low energy consumption when the relative speed between the shafts is high.